1. Field of the Invention
This invention concerns a system for increasing the conversion of carbon monoxide into carbon dioxide and more particularly in reactions H2O+CO=CO2+H2, used for example to prepare gas for the synthesis of ammonia and carried out in reactors with at least one bed formed by large size catalyst pellets compatible with the pressure drop resulting from the axial flow of the reaction gas.
The invention comprises also reactors so obtained by modifying them in situ.
2. Description of the Related Art
One of the fundamental operations in preparing synthesis gas for NH3 (N2+H2 mixture) is the conversion of CO into CO2 and H2 according to the following chemical reaction: EQU H2O+CO.revreaction.CO2+H2
This reaction, in modern ammonia production lines, takes place in two stages at a pressure of about 30.div.40 kg/cm2, namely:
1st stage at high temperature in which the gas is reacted on an iron oxide catalyst at a temperature of 350.div.400.degree. C. and in which the CO is converted from 17.div.20% mole on a dry basis to a residual 3%, still on a dry basis;
2nd stage at low temperature, at about 200.div.250.degree. C. and using a copper-based catalyst. During this second stage, given the lower temperature, the balance is directed towards the conversion of the carbon monoxide and it is possible to obtain very low CO residue (.apprxeq.0.3% mole on a dry basis) thus facilitating the depuration treatment which follows (elimination of CO2 by washing with suitable solvents, and elimination of residual CO by methanation or by washing with liquid nitrogen).
Conversion reactions take place in large axial-flow converters, with adiabatic operation (therefore increasing the temperature as a result of the exothermic reaction), usually not with full board and with a noticeable pressure drop, given the axial flow and the large amounts of gas involved.
The catalysts most widely used at present are in tablets with a medium or small granulometry. Small granulometry catalysts (for example 6.4.times.3.2 mm) are more active than medium granulometry catalysts (for example 9.5.times.4.7 mm).
Their use, however, is made difficult by the fact that in axial flow catalytic beds they involve a higher pressure drop.
A purpose of this invention is to provide a system which makes it possible to eliminate the foregoing troubles and to obtain a greater conversion of CO into CO2 in conventional reactors.
Another purpose of the invention is to obtain reactors allowing a greater conversion of CO into CO2 by modifying in situ conventional reactors.